Often the temperature resistance of a conventional dust filter limits its application as the temperature of a process utilizing the filter exceeds the temperature range of the filter. It is possible to achieve a high temperature application by using steel net, but often these filters do not withstand corrosive substances. Nets of other metals can also be used, but these are quite expensive. Typically the filter must also withstand abrasion and pressure impacts, which are used at regular intervals to clean it.
International Patent Application PCT/FI89/20 discloses a method of manufacturing an oriented fiber structure, in which it is most advantageous to use a double disc knitting machine, on account of its great manufacturing output. In accordance with this disclosure, two rows of needles knit loops in different directions, which form lateral channels, into which it is possible to feed reinforcing fibers. A corresponding textile product, the structure of which is similar to that shown in this international application, is known from British application publication 2 121 837.